#!/bin/bash

read -p "please input your grade: " u_grade
if [ -z $u_grade]
then
	echo " please input then range of 1-100 number"
	exit
fi

if echo $u_grade |grep -v "[0-9]" &>/dev/null
then
	echo "please input the range of 0-100 number "
	exit
fi
if (($u_grade >=90 && $u_grade<=100))
then
	echo "A"
elif (($u_grade >=80 && $u_grade<=89))
then
	echo "B"
elif (($u_grade >=70 && $u_grade<=79))
then 
	echo "C"
elif (($u_grade >=60 && $u_grade<=69))
then 
	echo "D"
elif (($u_grade >=0 && $u_grade<=59))
then
	echo "E"
else 
	echo "please input the range of 0-100 number"
fi 
